public class Paper {
    private final String title;      // 论文题目，长度至少为3个字符

    public Paper(String title) {
        this.title = title;
    }

    public String getTitle() {
        return this.title;
    }

    public String toString() {
        return this.title + " (" + this.getClass().getName() + ")";
    }}
// 三种类型的论文（包内私有类，假设构造函数调用父类构造）
class Thesis extends Paper {
    public Thesis(String title) {
        super(title);
    }}
class JournalPaper extends Paper {
    public JournalPaper(String title) {
        super(title);
    }}
class ConferencePaper extends Paper {
    public ConferencePaper(String title) {
        super(title);
    }}
